package crazy.interfacee;

public class Recursive
{
	public static void main(String[] args)
	{
		System.out.println(f(10)); 
	}
	
	public static int f(int n)
	{/*
		if (n == 0)
		{
			return 1;
		}
		else if (n == 1)
		{
			return 4;
		}
		else
		{
			return 2 * f(n - 1) + f(n - 2);
		}
	*/
		
	if (n == 20)
	{
		return 1;
	}
	else if(n == 21)
	{
		return 4;
	}else 
	{
		return f(n+2) - 2*f(n+1);
	}
	}

}
